[Coco] How does the cartridge port work, anyway?

[T. Franklin]

If memory serves... Isn't there a CART signal that when the cartridge is inserted, this signal is shorted to a "0" state and the CPU sees this bit during boot? The BIOS then knows the cartridge is inserted and calls the code at $c000 (or some predetermined address in the cart. address area) for initialization. I remember that you could grab the cartridge code by placing a small piece of tape over this signal to prevent the BIOS from calling the cartridge initialization code. Then you can grab the cart image with a short assembly program.

At least this is how I remember it. I'm old and the gray matter doesn't work as well as it used too.





-----Original Message-----
From: Phill Harvey-Smith [mailto:afra at ramoth.org.uk]
Sent: Friday, February 15, 2013 04:05 AM
To: 'CoCoList for Color Computer Enthusiasts'
Subject: Re: [Coco] How does the cartridge port work, anyway?

On 15/02/2013 06:50, Darren A wrote:> If the SAM/GIME is configured for RAM/ROM mode, then the device select> code which is produced for the cartridge address range (C000-FFEF)> results in the 74LS138 asserting the line that goes to the CTS* pin> (Cartridge Select) on the cartridge port. Inside the ROM pak, the> signal from the CTS* pin is typically connected to the ROM's Output> Enable pin, Chip Select pin or both.The other way that this can happen of course is if the cartridge has it's own address decoding and holds the "device select disable" line low it can pretty much override the internal memory decoding.This could for example be used to map an external ROM / RAM into thearea that the basic roms normally occupy.This method is much more complex to implement, and the majority of cartridges just use the CTS* pin.Likewise the SCS* pin is decoded to go active between $FF40 and $FF5F and is typically used to access the disk controller chip & registers.Cheers.Phill.--Coco mailing listCoco at maltedmedia.comhttp://five.pairlist.net/mailman/listinfo/coco